in the last week every morning when I unplug my fully recharged iPhone it switched off automatically.
when I switch on again the battery level showed is very low (generally 6%} some times it return 100% by itself, more times I have to switch off and on again (some times more than once) to have the right battery level shown.
[Re-Titled by Moderator]
iPhone 7
You're iPhone 7 is rather old and the battery is probably at the end of its life.
Batteries degrade over time with usage due to chemical aging.
You can expect about a 1% drop per month with average use on an iPhone. This is an approximation, that is why it may be plus or minus a few percent on a month to month basis.
Apple recommends replacing it when it reaches 80%. To check your battery health, go to Settings > Battery > Battery Health.
iPhone Battery Replacement.
iPhone Battery Replacement - Apple Support
About Lithium Ion Batteries
iPhone battery and performance - Apple Support (IN)
You're iPhone 7 is rather old and the battery is probably at the end of its life.
Batteries degrade over time with usage due to chemical aging.
You can expect about a 1% drop per month with average use on an iPhone. This is an approximation, that is why it may be plus or minus a few percent on a month to month basis.
Apple recommends replacing it when it reaches 80%. To check your battery health, go to Settings > Battery > Battery Health.
iPhone Battery Replacement.
iPhone Battery Replacement - Apple Support
About Lithium Ion Batteries
iPhone battery and performance - Apple Support (IN)
What does the Battery Health report?
iPhone shuts down after unplugging power cable even if it's full charged
